1. Field of the Invention
The invention relates to gas analyzing systems which measure periodic pressure variations occuring within an acoustically resonant gas sample contained within a sample chamber.
2. Description of the Priot Art
U.S. Pat. No. 3,005,097 disclosed a method and apparatus for analyzing mixtures of gases contained within a chamber. A beam of light is transmitted through the gas sample therein. The gas sample is subjected to periodic density variations produced by a reciprocating piston which is coupled to the chamber containing the gas. Variations in density within the chamber cause a periodic change in the light flux absorbed therein and transmitted therethrough into a gas contained within a second chamber. Gas heating within the second chamber is measured by transducing the change in capacitance produced by the deflection of a membrance which is part of a variable capacitor. The pressure transducer disclosed in U.S. Pat. No. 3,005,097 does not respond to pressure fluctuations induced within the gas sample at a frequency corresponding to an acoustical resonance of that gas sample in its container which is identical in frequency to the mechanical resonance of the deflecting diaphragm of the pressure transducer.
U.S. Pat. No. 2,951,938 discloses a gas analyzing system similar to that disclosed in U.S. Pat. No. 3,005,097. A source of energy is directed through a gas sample which is contained in a chamber that is divided into two parts by the membrance of a pressure transducer of the variable capacitance type. A source of radiation which impinges on the sample chamber is optically chopped at a frequency which produces vibrations of the diaphragm contained within the chamber if energy is absorbed within one of the parts of the chamber which is irradiated by the source of radiation. U.S. Pat. No. 2,951,938 discloses the use of a small leak between the two parts of the chamber to relieve slowly varying pressure differences which arise from a temperature differential between the two parts of the chamber without dissipating rapid pressure changes which cause the diaphragm to vibrate. However, the pressure transducer disclosed in U.S. Pat. No. 2,951,938 differs substantially from the present invention in that it does not respond to pressure fluctuations amplified by the action of an acoustic resonance within a chamber and detected by means of the enhanced displacement of a diaphragm whose mechanical resonance frequency matches that acoustical resonance frequency.